1. Field of the Invention
This invention relates to new heat curable mixtures, based on a polyisocyanate component containing blocked isocyanate groups and a reactive component containing primary amino groups, and to the use of the mixtures for the formation of coatings on heat resistant substrates.
2. Description of the Prior Art
The preparation of coating compositions based on ketoxime-blocked polyisocyanates and organic polyamines is described in DE-OS 1,544,813. These systems harden at temperatures above about 120.degree. C. but have the disadvantage of insufficient storage stability, especially in the absence of solvents. They also have the disadvantage that they can only be applied in comparatively thin layers.
DE-AS 2,131,299 describes a heat curable mixture of a polyisocyanate component containing isocyanate groups blocked with .epsilon.-caprolactam and cycloaliphatic polyamines. The systems described in the said prior publication have good storage stability and are suitable for the formation of thick coatings with superior mechanical properties. The disadvantage of these systems, however, is the comparatively high reaction temperatures of about 160.degree. C. required for curing.
It is an object of the present invention to provide new heat curable systems which result in coatings of superior quality even when applied in thick layers. It is an additional object of the present invention to provide heat curable systems which possess both good storage stability at room temperature and low stoving temperatures.
These objects may be achieved with the heat curable systems of the present invention as described hereinafter.